Functional class helps predict mortality risk after surgery

Functional classification adds useful information on surgical mortality risk -- beyond that provided by the routine American Society of Anesthesiologists (ASA) Physical Classification System, report Dr. Nader D. Nader and colleagues of University at Buffalo, N.Y. They write, "Functional classification was an independent predictor of mortality within each ASA class, indicating that it should be considered for incorporation into the routine preoperative evaluation."

Independent Functioning Predicts Better Surgical Outcomes

The study included more than 12,000 patients undergoing noncardiac surgery between 1998 and 2010, identified through a Veterans Affairs (VA) quality improvement database. Based on the widely used ASA functional classification, about 30 percent of patients were in ASA class II, with mild but well-controlled disease; 53 percent were in class III, denoting severe disease; 13 percent were in class IV, denoting severe, life-threatening disease; and one percent were in class V, including patients who are not expected to survive without surgery. (Another three percent of patients were in class I, denoting no health problems at all.)

The researchers also rated each patient's functional status, based on their ability to perform routine activities of daily living (ADLs) -- moving around, dressing, etc. Group A patients were completely independent in all ADLs, while group B patients were at least partially dependent on others. Not surprisingly, group B patients had more accompanying health problems, such as hypertension, diabetes, etc.

The results showed that patients who could perform all ADLs independently were at significantly lower risk of death. Short-term mortality rate was about two percent for group A patients versus 13 percent for those in group B.

In fact, group B patients in any ASA class were at higher risk of death than group A patients in the subsequent, sicker class. The odds of death were about 90 percent higher for group IIB patients versus IIIA patients, 30 percent higher for group IIIB versus IVA patients, and twice as high for group IVB versus group V patients.

After adjustment for other factors, group B patients were 4.5 times more likely to die within 30 days after surgery. Patients with any type of functional limitation were also at higher risk of complications, including myocardial infarction (heart attack), pneumonia, and reduced kidney function.

The ASA classification is a simple score for assessing preoperative health status, and is a reliable predictor of surgical mortality risk. However, in some groups of patients -- such as the very elderly and those undergoing vascular surgery -- the ASA system has limited value. That's because most of these patients are in ASA class III or IV and have multiple health problems.

Dr. Nader and coauthors write, "[A]dding functional capacity to traditional ASA classification improves its predictive value for short-term and long-term mortality and the occurrence of postoperative complications." They emphasize that even patients who appear "sicker" based on ASA class are at lower risk of death if they are functionally independent.

"Functional status assessment can be easily incorporated into the current ASA classification, as it can be assessed by patient interview alone and does not require any calculations, formulas, laboratory data, or diagnostic tests," Dr. Nader and colleagues add. One possible modification would be to increase the ASA class by one point for patients with any limitation in basic ADLs. However, the researchers emphasize the need for further studies in different patient populations.